Air filters positioned within or as part of an air intake system for an engine provide filtered air for the engine. Air filters can extract dust, dirt, and other air borne materials from an engine's air intake system so that air borne material does not collect in the engine and degrade engine performance and operation. However, air borne material can collect within the air filter over time such that the air filter restricts air flow into the engine. The air flow restriction from the air filter can increase engine pumping work and reduce vehicle fuel economy. In order to replace or clean the clogged air filter, a status of the air filter may be regularly diagnosed, and indicated to the operator.
Various approaches are provided for carrying out diagnostics of the intake air filter. In one example approach, as shown in U.S. Patent Application Publication No. 20110185895, Freen et al. shows a diagnostic method for an intake air filter to be carried out using a pressure sensing module including a battery powered pressure sensing probe coupled across the intake air filter. The pressure sensing probe measures a pressure differential between a first location, upstream of the air filter, and a second location, downstream of the air filter. Filter condition is then determined by comparing the pressure differential to a predetermined baseline pressure differential.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, in the system described by Freen, a battery powered probe is used to measure the pressure differential across the air filter which is generally not present around the air filter in naturally aspired engines. The additional probe may add complexity and cost to the engine system. Also, operation of the battery operated sensor may increase the parasitic loss of engine power due to the energy required to recharge the battery. Further, since re-calibration of the baseline pressure differential is to be carried out by a user whenever a new filter is installed, if the re-calibration is not timely performed, the described method may lead to incorrect estimation of filter condition. The air filter diagnosis depends on the engine being operational and intake air flowing into the engine. In a hybrid vehicle, however, the engine may operate for shorter durations. Thus, the air filter diagnostic may not be performed regularly causing the vehicle to operate with a clogged or blocked air filter for extended periods of time.
The inventors herein have recognized that the issues described above may be addressed by an engine method comprising: during unfueled cranking of an engine while the engine is spun in reverse, indicating a blocked intake air filter based on air flow through an exhaust system relative to air flow through an intake system and further based on a change in the air flow through the exhaust system upon opening a secondary path to atmosphere. In this way, by opportunistically spinning the engine in reverse direction during a vehicle key-off condition and monitoring air flow through the exhaust manifold and intake manifold, a blocked intake air filter may be diagnosed.
As one example, diagnostic routine of the intake air filter may be opportunistically carried out during vehicle key-off conditions when the engine is not operated and the vehicle is unoccupied. The diagnostic routine includes rotating the engine in a reverse direction via an electric machine and also spinning a battery operated electric booster coupled to the intake manifold in a reverse direction to draw in ambient air from the tailpipe and route the air to the intake manifold. Air flow through the exhaust passage is estimated via a differential pressure sensor coupled across a particulate filter and air flow through the intake passage is estimated via a manifold air flow (MAF) sensor. The exhaust air flow and the intake air flow may be compared to each other and then further compared to a baseline air flow. Upon installation of the intake air filter, the baseline air flow may be obtained by reverse rotating the engine and estimating air flow through the intake manifold via the MAF sensor. If it is determined that the intake air flow is substantially equal to each of the exhaust air flow and the baseline air flow, it may be indicated that the intake air filter is not blocked. If it is determined that the exhaust air flow is substantially equal to the intake air flow but is lower than the baseline air flow, a canister purge valve (CPV) and a canister vent valve (CVV) coupled to a canister purge line of an evaporative emissions control (EVAP) system may be opened to enable an alternate route for fluidic communication between the engine system and atmosphere. Upon opening of the CPV and the CVV, air entering through the exhaust manifold may be released to the atmosphere through the canister purge line without flowing through the portion of the intake passage housing the MAF sensor and the intake air filter. Therefore, if it is observed that the exhaust air flow increases to the baseline air flow without as significant change in the intake air flow, it may be inferred that the intake air filter is blocked and a diagnostic code may be set.
In this way, diagnostics of the intake air filter may be opportunistically carried out using components already existing in the engine system, thereby providing cost benefits. The technical effect of detecting a blockage in the intake air filter is that a desired air-fuel ratio may be maintained and combustion of richer than stoichiometric air-fuel mixture may be reduced. By maintaining the desired air-fuel ratio, fouling of spark plugs may be reduced and desired ignition timings may be maintained. Overall, by regularly monitoring the health of the intake air filter, degradation of the air filter may be detected in a timely manner and replacement of the blocked intake air filter may result in increased vehicle fuel economy and emissions quality.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.